Monkeys may be operantly trained to produce highly specific firing patterns from neocortical neurons, but operant control of single neurons, as a technique for investigating the central nervous system has not been fully realized. The potent advantage of this method is that the monkey is undrugged and an active participant in the experiments. This obviates variables which alter normal physiology in acute experiments. This proposal describes a standardized single unit conditioning paradigm capable of quantifying the monkey's control of physiologically identified single neurons in precentral cortex. Experiments are described which are aimed at determining a) differences in control over various groups of neurons, b) the limits of operant control over neurons, c) the role of proprioception and other sensory stimuli in the control of precentral neurons, and d) the differences in the degree of control between normal and epileptic neurons.